Inverse Trigonometry Formulas sin-1 (–x) = – sin-1 xcos-1 (–x) = π – cos-1 xtan-1 (–x) = – tan-1 xcosec-1 (–x) = – cosec-1 xsec-1 (–x) = π – sec-1 xcot-1 (–x) = π – cot-1 x